Pathica - Find a path to connect with anyone on Instagram.
Apache Lucene - High-performance, full-featured text search engine library written entirely in Java.
Endless - Random and amazing Wikipedia articles.
Six Degrees of Wikipedia - Find the shortest path between two subjects
Data Dashboard by Wikimedia Foundation - Compiled data of the Worlds busiest public site
Sphinx Search - Sphinx is an open source full text search server, designed with performance, relevance (search quality), and integration simplicity in mind. Sphinx lets you either batch index and search data stored in files, an SQL database, NoSQL storage.